overleaf/services/web/app/src/Features/FileStore/FileStoreController.js

const logger = require('@overleaf/logger')

const FileStoreHandler = require('./FileStoreHandler')
const ProjectLocator = require('../Project/ProjectLocator')
const Errors = require('../Errors/Errors')

module.exports = {
  getFile(req, res) {
    const projectId = req.params.Project_id
    const fileId = req.params.File_id
    const queryString = req.query
    const userAgent = req.get('User-Agent')
    ProjectLocator.findElement(
      { project_id: projectId, element_id: fileId, type: 'file' },
      function (err, file) {
        if (err) {
          logger.err(
            { err, projectId, fileId, queryString },
            'error finding element for downloading file'
          )
          return res.sendStatus(500)
        }
        FileStoreHandler.getFileStream(
          projectId,
          fileId,
          queryString,
          function (err, stream) {
            if (err) {
              logger.err(
                { err, projectId, fileId, queryString },
                'error getting file stream for downloading file'
              )
              return res.sendStatus(500)
            }
            // mobile safari will try to render html files, prevent this
            if (isMobileSafari(userAgent) && isHtml(file)) {
              res.setHeader('Content-Type', 'text/plain')
            }
            res.setContentDisposition('attachment', { filename: file.name })
            stream.pipe(res)
          }
        )
      }
    )
  },

  getFileHead(req, res) {
    const projectId = req.params.Project_id
    const fileId = req.params.File_id
    FileStoreHandler.getFileSize(projectId, fileId, (err, fileSize) => {
      if (err) {
        if (err instanceof Errors.NotFoundError) {
          res.status(404).end()
        } else {
          logger.err({ err, projectId, fileId }, 'error getting file size')
          res.status(500).end()
        }
        return
      }
      res.set('Content-Length', fileSize)
      res.status(200).end()
    })
  },
}

function isHtml(file) {
  return (
    fileEndsWith(file, '.html') ||
    fileEndsWith(file, '.htm') ||
    fileEndsWith(file, '.xhtml')
  )
}

function fileEndsWith(file, ext) {
  return (
    file.name != null &&
    file.name.length > ext.length &&
    file.name.lastIndexOf(ext) === file.name.length - ext.length
  )
}

function isMobileSafari(userAgent) {
  return (
    userAgent &&
    (userAgent.indexOf('iPhone') >= 0 || userAgent.indexOf('iPad') >= 0)
  )
}